rdelaage
/
postgresql
mirror of https://git.postgresql.org/git/postgresql.git
1
0
Fork 0
Code Issues Packages Projects Releases Wiki Activity

Fix costing for disk-based hash aggregation. 

Report and suggestions from Richard Guo and Tomas Vondra.

Discussion: https://postgr.es/m/CAMbWs4_W8fYbAn8KxgidAaZHON_Oo08OYn9ze=7remJymLqo5g@mail.gmail.com
This commit is contained in:
Jeff Davis 2020-03-28 10:53:01 -07:00
parent 4083f445c0
commit 7351bfeda3
2 changed files with 16 additions and 16 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
src/backend/executor/nodeAgg.c
View File

@ -1728,6 +1728,8 @@ hash_agg_set_limits(double hashentrysize, uint64 input_groups, int used_bits,
/* if not expected to spill, use all of work_mem */
if (input_groups * hashentrysize < work_mem * 1024L)
{
if (num_partitions != NULL)
*num_partitions = 0;
*mem_limit = work_mem * 1024L;
*ngroups_limit = *mem_limit / hashentrysize;
return;

30
src/backend/optimizer/path/costsize.c
View File

@ -2257,6 +2257,7 @@ cost_agg(Path *path, PlannerInfo *root,
*/
if (aggstrategy == AGG_HASHED || aggstrategy == AGG_MIXED)
{
double pages;
double pages_written = 0.0;
double pages_read = 0.0;
double hashentrysize;
@ -2264,7 +2265,7 @@ cost_agg(Path *path, PlannerInfo *root,
Size mem_limit;
uint64 ngroups_limit;
int num_partitions;
int depth;
/*
* Estimate number of batches based on the computed limits. If less
@ -2279,25 +2280,22 @@ cost_agg(Path *path, PlannerInfo *root,
nbatches = Max( (numGroups * hashentrysize) / mem_limit,
numGroups / ngroups_limit );
nbatches = Max(ceil(nbatches), 1.0);
num_partitions = Max(num_partitions, 2);
/*
* The number of partitions can change at different levels of
* recursion; but for the purposes of this calculation assume it stays
* constant.
*/
depth = ceil( log(nbatches) / log(num_partitions) );
/*
* Estimate number of pages read and written. For each level of
* recursion, a tuple must be written and then later read.
*/
if (nbatches > 1.0)
{
double depth;
double pages;
pages = relation_byte_size(input_tuples, input_width) / BLCKSZ;
/*
* The number of partitions can change at different levels of
* recursion; but for the purposes of this calculation assume it
* stays constant.
*/
depth = ceil( log(nbatches - 1) / log(num_partitions) );
pages_written = pages_read = pages * depth;
}
pages = relation_byte_size(input_tuples, input_width) / BLCKSZ;
pages_written = pages_read = pages * depth;
startup_cost += pages_written * random_page_cost;
total_cost += pages_written * random_page_cost;